Removing the flight crew from the country actually stops them being subpoenaed by the authorities. If they were thrown on a plane straight back to Dubai the ATSB would have a hard time actually talking to them if Emirates wanted to play hard ball. If they were in Australia then they would have a legal obligation to talk to the ATSB I would imagine.
This whole thing could become a political minefield as the airline is not a private company as such. So the owners may not be to appreciative of another government authority investigating their company.
As for LLZ it is aligned with the centreline. How else would you transmit a beam that tracks you down the centreline?